Quadrifilar helix antenna system with ground plane

Abstract

A quadrifilar helix antenna system with a finite ground plane has a pair of bifilar helical elements extending upwardly from the finite ground plane. A symmetrical array of monopole elements surrounds the lower portion of the pair of bifilar helical elements in the near field so as to load the lower portion and thereby raise the phase center of the antenna to improve the circularly polarized far-field radiation at low elevation angles.

The invention claimed is: 
     
       1. A quadrifilar helix antenna system with a finite electrically conductive ground plane, comprising:
 a pair of bifilar helical elements on a core extending upwardly from the ground plane; and 
 a symmetrical array of upstanding parasitic monopole elements electrically mounted on the finite electrically conductive ground plane and surrounding a lower portion of the pair of bifilar helical elements in the near field so as to load said lower portion and thereby raise the phase center of the antenna to improve the circularly polarized far-field radiation at low elevation angles. 
 
     
     
       2. A quadrifilar helix antenna system as claimed in  claim 1 , wherein the height and position of the parasitic monopole elements are configured such that the phase centers for different field components of the radiation are substantially lined up. 
     
     
       3. A quadrifilar helix antenna system as claimed in  claim 1 , wherein the height of the parasitic monopole elements is less than ¼ wavelength. 
     
     
       4. A quadrifilar helix antenna system as claimed in  claim 1 , wherein the parasitic monopole elements are spaced a distance between ⅙ th  of a wavelength and 1/10 th  of a wavelength from the core. 
     
     
       5. A quadrifilar helix antenna system claimed in  claim 1 , wherein the ground plane is less than one wavelength across. 
     
     
       6. A quadrifilar helix antenna system as claimed in  claim 1 , wherein the height and number/density of the parasitic monopole elements is selected such that it improves low elevation angle coverage without negatively affecting pattern symmetry. 
     
     
       7. A quadrifilar helix antenna system as claimed in  claim 2 , wherein the height of the parasitic monopole elements is about 0.6 the height of the antenna. 
     
     
       8. A quadrifilar helix antenna as claimed in  claim 1 , wherein the array of parasitic monopole elements comprises four upstanding monopole elements arranged at the corners of a square. 
     
     
       9. A quadrifilar helix antenna system as claimed in  claim 1 , wherein the parasitic monopole elements comprise upstanding conductive rods. 
     
     
       10. A quadrifilar helix antenna system as claimed in  claim 1 , wherein the finite ground plane forms part of a printed circuit board mounting electronic components. 
     
     
       11. A method of improving the performance of a quadrifilar helix antenna system with an electrically conductive finite ground plane at low elevation angles, comprising:
 surrounding a lower portion of a pair of bifilar helical elements on a core forming part of the antenna system with a symmetrical array of upstanding parasitic monopole elements in the near field, said parasitic monopole elements being electrically mounted on the finite electrically conductive finite ground plane; and 
 using the symmetrical array of upstanding parasitic monopole elements to load the lower portion and thereby raise the phase center of the antenna. 
 
     
     
       12. A method as claimed in  claim 11 , wherein the height and position of the parasitic monopole elements are configured such that the phase centers for different field components of the radiation are lined up. 
     
     
       13. A method as claimed in  claim 12 , wherein the height of the parasitic monopole elements is adjusted such that it improves low elevation angle coverage without negatively affecting pattern symmetry. 
     
     
       14. A method as claimed in  claim 11 , wherein the height of the parasitic monopole elements is less than ¼ wavelength. 
     
     
       15. A method as claimed in  claim 13 , wherein the height of the parasitic monopole elements is about 0.6 the height of the antenna. 
     
     
       16. A method as claimed in  claim 11 , wherein the parasitic monopole elements are spaced a distance between ⅙ th  of a wavelength and 1/10 th  of a wavelength from the core. 
     
     
       17. A method as claimed in  claim 11 , wherein the array of parasitic monopole elements comprises four upstanding monopole elements arranged at the corners of a square, wherein the diagonals of the square bisect the angle between adjacent termination points of the bifilar helical elements on the finite ground plane. 
     
     
       18. A method as claimed in  claim 11 , wherein the parasitic monopole elements comprise upstanding conductive rods. 
     
     
       19. A method as claimed in  claim 11 , wherein the finite ground plane forms part of a printed circuit board mounting electronic components. 
     
     
       20. A quadrifilar helix antenna system with a finite electrically conductive Ground plane, comprising:
 a pair of bifilar helical elements on a core extending upwardly from the ground plane; and 
 a symmetrical array of upstanding parasitic monopole elements on the finite electrically conductive ground plane having a height less than ¼ wavelength and surrounding a lower portion of the pair of bifilar helical elements in the near field so as to load said lower portion and thereby raise the phase center of the antenna to improve the circularly polarized far-field radiation at low elevation angles.